B. 12
Feedback Let the time taken by A to finish the work = x days
Then, time taken by B to finish the work = 2x days
Given, Time taken by A and B together ie., (A + B) = 8 days.
=>1/(A + B) = (1/A) + (1/B)
=> 1/8 = (1/x) + (1/2x)
=> 1/8 = (2 + 1) / 2x
=> 1/8 = 3/2x
Taking reciprocal on both sides,
=> 8 = 2x / 3
=> 8 * 3 = 2x
=> 24/ 2 = x
=>x = 12
A alone complete the work in 12 days.